Liquid pressure booster

ABSTRACT

A liquid pressure booster which may be used in a brake booster or the like is disclosed. A second supply passage is provided which allows a power chamber of the liquid pressure booster to communicate with an external source of pressure fluid without passing through a valve mechanism of the liquid pressure booster. A first open/close valve is operative to open or close the second supply passage, and a second open/close valve is effective to open or close a discharge passage of the liquid pressure booster. A controller controls the first and the second open/close valve. With this construction, the controller may be caused to open the first valve and to close the second valve to allow the pressure fluid to be introduced into the power chamber through the second supply passage without depressing a brake pedal to cause a forward movement of an input shaft. In this manner, the liquid pressure booster can be operated automatically, and thus such booster can be advantageously used in an automatic braking unit.

FIELD OF THE INVENTION

The invention relates to a liquid pressure booster which may be used ina brake booster or the like.

DESCRIPTION OF THE PRIOR ART

A conventional liquid pressure booster which may be used in a brakebooster, for example, generally comprises a power piston which isslidably disposed in a housing, a power chamber defined within thehousing on one side of the power piston, a stepped bore formed in thepower piston and including bore portions of a smaller and a largerdiameter with the bore of a larger diameter opening into the powerchamber, a supply passage for communicating the interior of the bore ofa smaller diameter communicating with a source of pressure fluid, afirst valve seat formed in the bore of a smaller diameter, a valveelement slidably disposed within the bore of a smaller diameter andadapted to be seated upon the first valve seat from the side nearer thesource of pressure fluid, an annular pin operated in interlockedrelationship with an input shaft for abutment against the valve elementfrom the side nearer the bore of a larger diameter to move it away fromthe first valve seat to thereby introduce a pressure fluid from thesource into the power chamber, a discharge passage formed in a shankportion of the annular pin for communicating the power chamber with areservoir, and a second valve seat formed on the free end of the annularpin for interrupting a communication between the power chamber and thedischarge passage upon abutment of the annular pin against the valveelement.

Generally, the end of the valve element opposite from that end which isadapted to be seated upon the first valve seat extends through secondseal means into a balance chamber, and a pressure chamber is definedbetween the second seal means and the first valve seat and communicateswith the supply passage. The balance chamber communicates with the powerchamber through a communication opening which is formed in the powerpiston.

In the liquid pressure booster mentioned above, when a brake pedal isreleased, the annular pin is spaced from the valve element to therebyallow the power chamber to communicate with the reservoir through thedischarge passage, and the valve elements is seated upon the first valveseat to close the pressure chamber to which the pressure fluid issupplied.

By contrast, when the brake pedal is depressed and the annular pincauses the valve element to be moved away from the first valve seat, thesecond valve seat which is formed on the free end of the annular pinbecomes seated upon the valve element, whereby the communication betweenthe power chamber and the reservoir is interrupted. As the valve elementmoves away from the first valve seat, the pressure fluid is allowed tobe admitted into the power chamber, whereby the power piston can beadvanced under a fluid pressure.

At this time, the fluid pressure which is introduced into the powerchamber can be fed to the balance chamber through the communicationopening, whereby forces acting upon the valve element can be balanceddespite pressure fluctuations if a pressure responsive area of the valveelement on the side nearer the power chamber is chosen to be equal to apressure responsive area thereof on the side nearer the balance chamber.

In the conventional liquid pressure booster, there is no advancing ofthe power piston under normal condition where the brake pedal isreleased. In other words, there has been no idea of operating the liquidpressure booster when the brake pedal is released.

In the conventional liquid pressure booster, the first valve seat formedwithin the bore of a smaller diameter is defined by providing an annularmember which is a press fit in this bore. However, since this bore islocated inside the bore of a larger diameter and since it is requiredthat the axial size of the annular member be reduced in order to reducethe axial size of the liquid pressure booster, it is troublesome todispose the annular member as a press fit into the bore of a smallerdiameter formed in the power piston. In addition, there is a likelihoodthat the pressure liquid may leak between the outer surface of theannular member and the inner surface of the bore of a smaller diameter.

In addition, when forming the communication opening which provides acommunication between the balance chamber and the power chamber in thepower piston, it is necessary that a radial passage extending from thebalance chamber radially outward of the power piston and an axialpassage communicating with this radial passage be provided to define thecommunication opening.

When the radial passage is to be formed by a drilling operation, suchradial passage must be drilled through the outer peripheral surface ofthe power piston with consequence that the resulting opening must besealed by a plug member such as a ball. This results in a complicatedconstruction and also involves the likelihood that the plug member maybe disengaged.

On the other hand, another arrangement is proposed in which a recesswhich corresponds to the radial passage is formed in the end face of apush rod at its one end while the axial passage mentioned above isarranged to open into the free end of the power piston, with suchopening being covered by the above mentioned end face of the push rod,thus allowing the axial passage to communicate with the recess. However,this arrangement is again complicated in construction and is thereforeexpensive to provide.

SUMMARY OF THE INVENTION

In view of the foregoing, the invention relates to a liquid pressurebooster which is known in itself. Specifically, such booster comprises apower piston slidably disposed in a housing, a power chamber definedwithin a housing on one side of the power piston, a valve mechanismdisposed in the power piston for switching a fluid path in response tothe operation of an input shaft, a first supply passage providing acommunication between the power chamber and a source of pressure fluidthrough the valve mechanism, and a discharge passage for providing acommunication between the power chamber and a reservoir through thevalve mechanism. In accordance with the invention, there are alsoprovided a second supply passage which allows the power chamber tocommunicate with the source of pressure fluid without passing throughthe valve mechanism, a first and a second open/close valve which open orclose the second supply passage and the discharge passage, respectively,and a controller for controlling the operation of the first and thesecond valve.

With this construction, the controller operates to close the first valvewhile maintaining the second valve open under a normal condition, thusallowing a pressure fluid to be supplied into the power chamber withoutpassing through the second supply passage. Since the discharge passageremains open, there occurs the same operation as that occurring in aconventional liquid pressure booster.

By contrast, when the controller operates to open the first valve and toclose the second valve, the pressure fluid can be introduced into thepower chamber through the second supply passage, and the pressure fluidwhich has been introduced into the power chamber cannot be discharged tothe reservoir through the discharge passage, so that the power pistonmay be advanced without driving the input shaft forward by thedepression of a brake pedal or the like. In this manner, the liquidpressure booster may be utilized as an actuator for an automatic brakingunit.

A liquid pressure booster including the valve mechanism mentioned abovemay also be modified in accordance with another aspect of the inventionby providing a stepped sleeve including portions of a smaller and alarger diameter which are fitted into the bores of a smaller and alarger diameter formed in the power piston, respectively. Securing meansfixedly connects the larger diameter portion of the stepped sleeve tothe power piston while the first valve seat is formed on the free end ofthe smaller diameter portion of the stepped sleeve to allow the valveelement to be seated thereupon. First seal means is disposed to maintaina liquid tightness between the smaller diameter portion of the sleeveand the bore of a smaller diameter.

When the stepped sleeve is fitted into the stepped bore formed in thepower piston and the larger diameter portion of the sleeve is fixedlyconnected to the power piston by securing means such as a lock nut or bycaulking, it will be seen that since the larger diameter portion islocated outward of the smaller diameter portion, the assemblingoperation can be facilitated as compared with providing the annularmember which is to be placed as a press fit into the bore of a smallerdiameter as occurring in the prior art. In addition, the provision ofthe first seal means which seals a clearance between the smallerdiameter portion of the sleeve and the bore of a smaller diameterreliably prevents a leakage of pressure fluid.

According to a further aspect of the invention, the supply passagecomprises an opening formed to extend through the outer peripheralsurface of the power piston and extending into the bore of a smallerdiameter along an oblique path. The communicatin opening which providesa communication between the balance chamber and the power chambercomprises a first communication opening formed on an extension of theoblique opening formed in the power piston, and a second communicationopening formed axially of the power piston. In addition, second sealmeans is disposed between the oblique opening and the firstcommunication opening to interrupt a communication therebetween.

With this construction, the first communication opening, whichcorresponds to the radial passage used in the prior art, is formed on anextension of the oblique opening which defines the supply passage, andaccordingly the first communication opening does not open into the outerperipheral surface of the power piston as occurring when the firstcommunication opening is formed in the opposite direction from the outerperipheral surface of the power piston. In this manner, a plug memberwhich is required to seal the resulting opening can be dispensed with,simplifying the construction and avoiding the likelihood ofdisengagement of such plug member.

Above and other objects and features of the invention will becomeapparent from the following description of an embodiment thereof withreference to the attached drawing.

BRIEF DESCRIPTION OF THE DRAWING

A single drawing is a perspective view, partly in longitudinal section,of one embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENT

Referring to the drawing, an embodiment of the invention will now bedescribed. A liquid pressure booster includes a housing 1 in which abore 1a of a larger diameter is formed along its axis. A power piston 2has a right portion 2a of a larger diameter which is slidably fitted inthe bore 1a. The power piston 2 also includes a left portion 2b of asmaller diameter which slidably extends through an opening 1b formed inthe left end wall of the housing, with a seal member 3 maintaining adust tightness thereat. The free end of the left portion 2b isintegrally formed with an output shaft 4 which is connected to a pistonof a master cylinder, not shown.

At its right end, the opening of the bore 1a is closed by a plug 11,which is secured to the housing 1 by an annular nut 12. A power chamber13 is defined between the plug 11 and the power piston 2 for admitting apressure oil therein. A low pressure chamber 14 is defined on theopposite side of the power piston 2 from the power chamber 13, and aspring 15 is disposed therein for normally maintaining the power piston2 in its inoperative position where it abuts against the plug 11. Thechamber 14 communicates with an atmosphere. A passage 16 which is formedin the housing 1 communicates with a reservoir 18 through a conduit 17.

The right end of the power piston 2 is axially formed with a steppedbore having a closed bottom, the stepped bore including a bore 2c of alarger diameter which opens into the power chamber 13. The power piston2 also includes a bore 2d of a smaller diameter, and a stepped sleeve 21has portions 21a and 21b of a smaller and a larger diameter,respectively, which are fitted into the bores 2d, 2c, respectively,formed in the power piston. A stop ring 22 and a sleeve 23 aresequentially fitted into a portion of the bore 2c which is located tothe right of the piston portion 21b of a larger diameter. At its rightend, the bore 2c is formed with female threads, which are engaged by alock nut 24 to secure the sleeve 23 in place. The lock nut 24 is securedto the power piston 2 by a punch caulking, not shown.

A first valve seat 28, which forms a valve mechamism 27, is formed onthe free end of the portion 21a of a smaller diameter of the sleeve 21,and a valve element 29 disposed to the left of the valve seat 28 isurged by a spring 30 to be seated upon the valve seat. Seal means 31such as O-ring which is disposed in the outer peripheral surface of theportion 21a seals between the outer surface of the portion 21a and theinner surface of the bore 2d, thereby allowing a communication betweenthe power chamber 13 and a pressure chamber 32, which are disposed tothe right and to the left of the first valve seat 28, respectively, tobe completely interrupted when the valve element 29 is seated upon thefirst valve seat 28.

As described, in the present embodiment, the stepped sleeve 21, the stopring 22 and the sleeve 23 are sequentially fitted into the stepped boreformed in the power piston 2, and the outermost member in the steppedbore, namely, the sleeve 23 is secured in place by means of the lock nut24 and the punch caulking in order to provide the first valve seat 28within the bore 2d of a smaller diameter. Accordingly, as compared withan arrangement in which an annular member is disposed in the bore 2d asa press fit therein to provide a corresponding first valve seat 28, theassembling operation can be facilitated. In addition, the seal means 31which seals the clearance between the small diameter portion 21a of thestepped sleeve 21 and the bore 2d improves in reliably preventing aleakage of pressure fluid as compared with the annular member which isdisposed as a press fit.

Second seal means 35 is disposed within the bore 2d to the left of thefirst valve seat 28, defining the pressure chamber 32 between the secondseal means 35 and the first valve seat 28. A balance chamber 36 isdefined to the left of the second seal means 35, and communicates withthe power chamber 13 through a communication opening 37 and an annulargroove 38 formed in the power pistion 2 and a hole 39 formed in thestepped sleeve 21.

The left end of the valve element 29 slidably extends through the secondseal means 35, which functions to maintain a liquid tightness, into thebalance chamber 36. By choosing a pressure responsive area of the valveelement 29 as measured on the side nearer the balance chamber 36 to besubstantially equal to a pressure responsive area of the valve element29 as measured on the side nearer the power chamber 13, any fluctuationin the pressure within the power chamber 13 and the balance chamber 36can be prevented from causing a displacement of the valve element 29.

The pressure chamber 32 communicates with an accumulator 45 through apassage 41 formed in the power piston 2, an annular groove 42 formedaround the outer peripheral surface of the power piston 2, a radialpassage 43 formed in the housing 1 and a conduit 44 connected to thepassage 43. The accumulator 45 communicates with a pump 47 through acheck valve 46. Accordingly, in the present embodiment, a first supplypassage 48 which provides a communication between the pump 47, servingas a source of pressure fluid, and the power chamber 13 through thevalve mechanism 27 comprises the conduit 44, the passage 43, the annulargroove 42, the passage 41 and the pressure chamber 32.

The passage 41 is formed as an opening which extends from the outerperipheral surface of the power piston 2 into the bore 2d along anoblique path, and the communication opening 37 which provides acommunication between the balance chamber 36 and the power chamber 13 isformed by a first communication opening 37a formed on an extension ofthe passage 41 and a second communication opening 37b which extendsaxially of the power piston 2. The second seal means 35 is disposedbetween the passage 41 and the first communication opening 37a tointerrupt a communication therebetween or a communication between thepressure chamber 32 and the balance chamber 36. When the firstcommunication opening 37a is formed on an extension of the passage 41,it is unnecessary that the first communication opening 37a opens intothe outer peripheral surface of the power piston 2 as would be requiredif the first communication opening 37a is formed by drilling through theouter peripheral surface of the power piston 2 in the reverse direction,and accordingly there is no need to provide a plug member which closesthe resulting opening. In this manner, the construction is simplifiedand the likelihood that the plug member may be disengaged is avoided.

An opening 11a is formed in the plug 11 in axial alignment with the bore1a formed in the housing 1, and an input shaft 49 which is mechanicallycoupled to a brake pedal, not shown, is slidably fitted in the opening11a. At its free end, the input shaft 49 is formed with a radiallyoutwardly extending flange 49a, with an annular pin 50, forming part ofthe valve mechanism 27, attached to the axial portion of the flange 49a.The flange 49a of the input shaft 49 is positioned within the portion21b of a larger diameter of the stepped sleeve 21, and is prevented frombeing disengaged from within the bore 2c formed in the power piston 2 tothe right, by the stop ring 22 which is disposed to the right thereof.

Since the stop ring 22 is held sandwiched between the stepped sleeve 21and the sleeve 23, the stop ring 22 can be positioned and held in placein a more reliable manner than when the stop ring 22 comprises a snapring which is positioned by engaging with an annular groove formed inthe inner peripheral surface of the power piston 2, as found in theprior art. However, it is also possible that the stepped sleeve 21 andthe sleeve 23 be formed integrally, with the stop ring 22 mounted in anannular groove which is formed in the inner peripheral surface of thesleeve 23.

In the inoperative condition shown in which a brake pedal, not shown, isreleased, a spring 51 disposed between the input shaft 49 and thestepped sleeve 21 urges the input shaft to the right, whereby the flange49a is maintained in its inoperative position shown where it abutsagainst the inner end face of the plug 11.

Under this condition, the annular pin 50 is spaced from the valveelement 29, and a passage 54 which is formed to extend through the axialportion of the annular pin 50 communicates with the power chamber 13,and also communicates with the reservoir 18 through a noise suppressingorifice 55 which is formed internally therein, an axial passage 56 and aradial passage 57 which are formed in the axial portion of the inputshaft 49, an annular groove 58 formed in the inner peripheral surface ofthe opening 11a formed in the plug 11, a radial passage 59 formed in theplug 11, an axial passage 60 formed in the housing 1 and the passage 16and the conduit 17 both mentioned above, whereby the power chamber 13 ismaintained in communication with the reservoir 18. Accordingly, in thepresent embodiment, a discharge passage 61 which communicates the powerchamber 13 with the reservoir 18 comprises a variety of passages whichare located between the passage 54 formed in the annular pin 50 and theconduit 17.

What has been described above relates to the inoperative condition.However, when a brake pedal is depressed to drive the input shaft 49forward, the valve element 29 will be seated upon a second valve seat 64which is formed on the free end of the annular pin 50 to interrupt thecommunication between the passage 54 and the power chamber 13 while theannular pin 50 forcibly moves the valve element 29 away from the firstvalve seat 28 against the resilience of the spring 30. As a consequence,the pressure oil which has been introduced into the pressure chamber 32will pass through a clearance between the outer periphery of the annularpin 50 and the inner periphery of the stepped sleeve 21 into the powerchamber 13, and such pressure oil introduced into the power chamber 13is effective to drive the power piston 2 to the left at a given boosterratio to provide a braking action, generally in a similar manner asoccurring in a conventional liquid pressure booster.

In the present embodiment, a conduit 65 has its one end connected to theconduit 44 which is disposed downstream of the accumulator 45, and theother end of the conduit 65 is connected to a radial passage 66 formedin the housing 1. The passage 66 opens into the bore 1a at a locationadjacent to the plug 11 and is maintained in communication with thepower chamber 13. Accordingly, in the present embodiment, a secondsupply passage 67 which allows the power chamber 13 to communicatedirectly with the pump 47 without passing through the valve mechanism 27comprises the passage 66, the conduit 65 and the conduit 44.

An annular notch 2e is formed around the periphery of the largerdiameter portion 2a of the power piston 2 adjacent to its free end inorder to prevent the opening of the passage 66 from being closed by theperipheral portion of the power piston 2 when the power piston 2 assumesits inoperative position shown.

Intermediate the length of the conduit 65 which forms the second supplypassage 67, a first open/close valve 68 is disposed at an upstreamposition or near the pump 47 and a pressure regulating valve 69 isdisposed downstream of the valve 68. The valve 68 is controlled by acontroller 70, which is also effective to change the pressure set-up ofthe regulating valve 69. A second open/close valve 71 is disposed in theconduit 17 which forms the discharge passage 61, and is also controlledby the controller 70.

Connected to the controller 70 is a detector 72 such as a vehicle speeddetector which is operative to detect a parking condition of a vehicle,an acceleration detector which serves detecting the depression of anaccelerator pedal or an inclinometer which detects an inclined attitudeof a vehicle for detecting a condition under which the first valve 68and the second valve 71 are to be opened or closed.

In the described arrangement, the controller 70 normally closes thefirst valve 68 disposed in the second supply passage 67 and opens thesecond valve 71 disposed in the discharge passage 61. Under thiscondition, the resulting arrangement is similar to a conventional liquidpressure booster which is devoid of the second supply passage 67 and thesecond valve 71, and hence operates in the similar manner as in aconventional booster.

By contrast, when the controller 70 determines that a condition prevailsunder which the liquid pressure booster is to be operated automatically,by comparing a result of detection by the detector 72 against apre-stored condition, it opens the first valve 68 in the second supplypassage 67 and closes the second valve 71 in the discharge passage 61.Thereupon pressure fluid is introduced into the power chamber 13 throughthe second supply passage 67, whereby the power piston 2 is driven tothe left to provide a braking action without the depression of a brakepedal.

At this time, the controller 70 is able to adjust the fluid pressureintroduced into the power chamber 13, and hence the braking force, bychanging the pressure set-up of the regulating valve 69. Accordingly,the pressure set-up may be modified in response to a signal from aninclinometer which detects an inclined attitude of a vehicle oralternatively the fluid pressure can be increased if the introduction ofa standard fluid pressure is ineffective to prevent a movement of thevehicle.

Subsequently when the controller 70 determines that a condition prevailsunder which the automatic braking action is to be released on the basisof an input from the detector 72, it closes the first valve 68 and opensthe second valve 71, thereby allowing the pressure fluid which has beenintroduced into the power chamber 13 to be discharged to the reservoir18 through the discharge passage 61, thus terminating the brakingaction.

While the invention has been described above in connection with thepreferred embodiment thereof, it should be understood that a number ofchanges, modifications and substitutions therein will readily occur toone skilled in the art from the above disclosure without departing fromthe spirit and scope of the invention defined by the appended claims.

What is claimed is:
 1. A liquid pressure booster including a powerpiston slidably disposed in a housing, a power chamber defined withinthe housing on one side of the power piston, a valve mechanism disposedin the power piston for switching a fluid path therein in response to anoperation of an input shaft, a first supply passage which provides acommunication between the power chamber and a source of pressure fluidthrough the valve mechanism and a discharge passage which provides acommunication between the power chamber and a reservoir through thevalve mechanism;characterized by a second supply passage which providesa communication between the power chamber and the source of pressurefluid without passing through the valve mechanism, a first open/closevalve for opening and closing the second supply passage, a secondopen/close valve for opening and closing the discharge passage, and acontroller for controlling the first and the second open/close valves.2. A liquid pressure booster according to claim 1, further including apressure regulating valve disposed downstream of the first open/closevalve in the second supply passage and having a pressure set-up which ismodified by the controller.
 3. A liquid pressure booster according toclaim 1, further including a detector for detecting a condition underwhich the first and the second open/close valves are to be operated, thecontroller being responsive to a detection signal from the detector tocontrol the first and the second open/close valves.